Hardware CRC Calculation functions.
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Hardware CRC Calculation functions.
===============================================================================
##### Hardware CRC Calculation functions #####
===============================================================================
[..] This section provides a set of functions allowing to manage the SPI CRC hardware
calculation
[..] SPI communication using CRC is possible through the following procedure:
(#) Program the Data direction, Polarity, Phase, First Data, Baud Rate Prescaler,
Slave Management, Peripheral Mode and CRC Polynomial values using the SPI_Init()
function.
(#) Enable the CRC calculation using the SPI_CalculateCRC() function.
(#) Enable the SPI using the SPI_Cmd() function
(#) Before writing the last data to the TX buffer, set the CRCNext bit using the
SPI_TransmitCRC() function to indicate that after transmission of the last
data, the CRC should be transmitted.
(#) After transmitting the last data, the SPI transmits the CRC. The SPI_CR1_CRCNEXT
bit is reset. The CRC is also received and compared against the SPI_RXCRCR
value.
If the value does not match, the SPI_FLAG_CRCERR flag is set and an interrupt
can be generated when the SPI_I2S_IT_ERR interrupt is enabled.
[..]
(@) It is advised not to read the calculated CRC values during the communication.
(@) When the SPI is in slave mode, be careful to enable CRC calculation only
when the clock is stable, that is, when the clock is in the steady state.
If not, a wrong CRC calculation may be done. In fact, the CRC is sensitive
to the SCK slave input clock as soon as CRCEN is set, and this, whatever
the value of the SPE bit.
(@) With high bitrate frequencies, be careful when transmitting the CRC.
As the number of used CPU cycles has to be as low as possible in the CRC
transfer phase, it is forbidden to call software functions in the CRC
transmission sequence to avoid errors in the last data and CRC reception.
In fact, CRCNEXT bit has to be written before the end of the transmission/reception
of the last data.
(@) For high bit rate frequencies, it is advised to use the DMA mode to avoid the
degradation of the SPI speed performance due to CPU accesses impacting the
SPI bandwidth.
(@) When the STM32F4xx is configured as slave and the NSS hardware mode is
used, the NSS pin needs to be kept low between the data phase and the CRC
phase.
(@) When the SPI is configured in slave mode with the CRC feature enabled, CRC
calculation takes place even if a high level is applied on the NSS pin.
This may happen for example in case of a multi-slave environment where the
communication master addresses slaves alternately.
(@) Between a slave de-selection (high level on NSS) and a new slave selection
(low level on NSS), the CRC value should be cleared on both master and slave
sides in order to resynchronize the master and slave for their respective
CRC calculation.
(@) To clear the CRC, follow the procedure below:
(#@) Disable SPI using the SPI_Cmd() function
(#@) Disable the CRC calculation using the SPI_CalculateCRC() function.
(#@) Enable the CRC calculation using the SPI_CalculateCRC() function.
(#@) Enable SPI using the SPI_Cmd() function.
===============================================================================
##### Hardware CRC Calculation functions #####
===============================================================================
[..] This section provides a set of functions allowing to manage the SPI CRC hardware
calculation.
[..] SPI communication using CRC is possible through the following procedure:
(#) Program the Data direction, Polarity, Phase, First Data, Baud Rate Prescaler,
Slave Management, Peripheral Mode and CRC Polynomial values using the SPI_Init()
function.
(#) Enable the CRC calculation using the SPI_CalculateCRC() function.
(#) Enable the SPI using the SPI_Cmd() function
(#) Before writing the last data to the TX buffer, set the CRCNext bit using the
SPI_TransmitCRC() function to indicate that after transmission of the last
data, the CRC should be transmitted.
(#) After transmitting the last data, the SPI transmits the CRC. The SPI_CR1_CRCNEXT
bit is reset. The CRC is also received and compared against the SPI_RXCRCR
value.
If the value does not match, the SPI_FLAG_CRCERR flag is set and an interrupt
can be generated when the SPI_I2S_IT_ERR interrupt is enabled.
[..]
(@)
(+@) It is advised to don't read the calculate CRC values during the communication.
(+@) When the SPI is in slave mode, be careful to enable CRC calculation only
when the clock is stable, that is, when the clock is in the steady state.
If not, a wrong CRC calculation may be done. In fact, the CRC is sensitive
to the SCK slave input clock as soon as CRCEN is set, and this, whatever
the value of the SPE bit.
(+@) With high bitrate frequencies, be careful when transmitting the CRC.
As the number of used CPU cycles has to be as low as possible in the CRC
transfer phase, it is forbidden to call software functions in the CRC
transmission sequence to avoid errors in the last data and CRC reception.
In fact, CRCNEXT bit has to be written before the end of the transmission/reception
of the last data.
(+@) For high bit rate frequencies, it is advised to use the DMA mode to avoid the
degradation of the SPI speed performance due to CPU accesses impacting the
SPI bandwidth.
(+@) When the STM32F30x are configured as slaves and the NSS hardware mode is
used, the NSS pin needs to be kept low between the data phase and the CRC
phase.
(+@) When the SPI is configured in slave mode with the CRC feature enabled, CRC
calculation takes place even if a high level is applied on the NSS pin.
This may happen for example in case of a multislave environment where the
communication master addresses slaves alternately.
(+@) Between a slave deselection (high level on NSS) and a new slave selection
(low level on NSS), the CRC value should be cleared on both master and slave
sides in order to resynchronize the master and slave for their respective
CRC calculation.
[..]
(@) To clear the CRC, follow the procedure below:
(#@) Disable SPI using the SPI_Cmd() function.
(#@) Disable the CRC calculation using the SPI_CalculateCRC() function.
(#@) Enable the CRC calculation using the SPI_CalculateCRC() function.
(#@) Enable SPI using the SPI_Cmd() function.
Enables or disables the CRC value calculation of the transferred bytes.
- Parameters
-
SPIx | where x can be 1, 2, 3, 4, 5 or 6 to select the SPI peripheral. |
NewState | new state of the SPIx CRC value calculation. This parameter can be: ENABLE or DISABLE. |
- Return values
-
- Parameters
-
SPIx | where x can be 1, 2 or 3 to select the SPI peripheral. |
NewState | new state of the SPIx CRC value calculation. This parameter can be: ENABLE or DISABLE. |
- Return values
-
Definition at line 907 of file stm32f4xx_spi.c.
void SPI_CRCLengthConfig |
( |
SPI_TypeDef * |
SPIx, |
|
|
uint16_t |
SPI_CRCLength |
|
) |
| |
Configures the CRC calculation length for the selected SPI.
- Parameters
-
SPIx | where x can be 1, 2 or 3 to select the SPI peripheral. |
SPI_CRCLength | specifies the SPI CRC calculation length. This parameter can be one of the following values:
- SPI_CRCLength_8b: Set CRC Calculation to 8 bits
- SPI_CRCLength_16b: Set CRC Calculation to 16 bits
|
- Return values
-
Definition at line 964 of file stm32f30x_spi.c.
uint16_t SPI_GetCRC |
( |
SPI_TypeDef * |
SPIx, |
|
|
uint8_t |
SPI_CRC |
|
) |
| |
Returns the transmit or the receive CRC register value for the specified SPI.
- Parameters
-
SPIx | where x can be 1, 2, 3, 4, 5 or 6 to select the SPI peripheral. |
SPI_CRC | specifies the CRC register to be read. This parameter can be one of the following values:
- SPI_CRC_Tx: Selects Tx CRC register
- SPI_CRC_Rx: Selects Rx CRC register
|
- Return values
-
The | selected CRC register value.. |
- Parameters
-
SPIx | where x can be 1, 2 or 3 to select the SPI peripheral. |
SPI_CRC | specifies the CRC register to be read. This parameter can be one of the following values:
- SPI_CRC_Tx: Selects Tx CRC register
- SPI_CRC_Rx: Selects Rx CRC register
|
- Return values
-
The | selected CRC register value.. |
Definition at line 947 of file stm32f4xx_spi.c.
Returns the CRC Polynomial register value for the specified SPI.
- Parameters
-
SPIx | where x can be 1, 2, 3, 4, 5 or 6 to select the SPI peripheral. |
- Return values
-
The | CRC Polynomial register value. |
- Parameters
-
SPIx | where x can be 1, 2 or 3 to select the SPI peripheral. |
- Return values
-
The | CRC Polynomial register value. |
Definition at line 972 of file stm32f4xx_spi.c.
Transmit the SPIx CRC value.
Transmits the SPIx CRC value.
- Parameters
-
SPIx | where x can be 1, 2, 3, 4, 5 or 6 to select the SPI peripheral. |
- Return values
-
- Parameters
-
SPIx | where x can be 1, 2 or 3 to select the SPI peripheral. |
- Return values
-
Definition at line 929 of file stm32f4xx_spi.c.